Economizer control

ABSTRACT

An economizer control for controlling air quality. The economizer control includes a sensor that senses characteristics of air, a damper located relative to the sensor so that the damper can control air flow of outside air and re-circulated air to the sensor, and a controller in communication with the sensor and the damper. The controller controls the opening and closing of the damper according to conditions sensed by the sensor.

PRIORITY

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/352,857, filed on Feb. 1, 2002. The aforementionedapplication is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to an improved economizercontrol of HVAC (Heating, Ventilation and Air Conditioning) systems.More particularly, the present invention relates to an improvedeconomizer HVAC system control resulting in increased energy efficiencyand a more comfortable environment than current economizer controlsprovide, while also ensuring good indoor air quality.

BACKGROUND OF THE INVENTION

[0003] A unitary heating, ventilation and air conditioning [Hereafterunitary HVAC] system is one type of HVAC system that is deemed “unitary”because it is generally configured in an integrated manner so that thisone system provides heating, cooling and air movement in a singlepackage. This unitary HVAC system can easily be placed on the rooftop ofa building. In a typical system, air intake dampers are adjusted toprovide a fixed outside air component to air circulated through thesystem. The amount of outside air required is usually determined bydetermining the design occupancy of the space and multiplying this timesa cfm/person (cfm=cubic feet per minute) recommended ventilation raterequired by local codes and standards. Typically, most spaces require 15cfm per person. This amount of outside air is determined by a designengineer and adjusted by the contractor that actually performsinstallation of the system. Typically, this adjustment of the outsideair intake results in a 20% to 30% mix of outside air together withrecirculated air.

[0004] Another common type of HVAC system is the unit ventilator. Unitventilators are a smaller version of unitary air handling equipment thathave been designed to serve a single space. Rather than being rooftopmounted, these devices are typically mounted through a wall and arepopular in applications such as servicing the HVAC needs of schoolclassrooms and hotel rooms. These devices, like the unitary HVAC, arealso integrated units designed to provide heating, cooling andventilation. The unit ventilator, however, services the heating andcooling requirements for a more limited area than a unitary system can.Unit ventilators are popular because they have a lower initial cost thana centralized system and they allow for specific control of a singlezone. Unit ventilator systems can be operated continuously or on an asneeded basis for both heating and cooling.

[0005] Most HVAC systems are only capable of being controlled based ontemperature and occupancy (manual turn off/on or timed operation).Humidity control has not been historically a consideration and mostmanufacturers do not have strategies for dealing with humidity. Finally,accurate, dependable and low cost humidity sensors have not beenavailable on the marketplace that have the low-cost, low maintenance andlong life characteristics demanded by these applications.

[0006] The combination of all the factors above have resulted in theincreased manifestation of unwanted growth of mold, mildew and otherbacterial entities in indoor spaces that can compromise the quality ofindoor air and the health of building occupants. The presence ofexcessive moisture can also result in the deterioration of physicalcomponents of a building including drywall, ceilings and woodenstructural components.

SUMMARY OF THE INVENTION

[0007] It is therefore a feature and advantage of the present inventionto provide an economizer control for controlling the air quality for aspace. In one embodiment of the invention, the economizer controlincludes a sensor that senses characteristics of air, a damper locatedrelative to the sensor so that the damper can control air flow ofoutside air and re-circulated air to the sensor, and a controller incommunication with the sensor and the damper. The controller controlsthe opening and closing of the damper according to conditions sensed bythe sensor.

[0008] In another embodiment of the invention a method for controllingan economizer includes the steps of sensing characteristics of air; andcontrolling a damper to control the air flow of outside air andre-circulated air in accordance with the sensed characteristics of theair.

[0009] In an alternate embodiment of the invention, a system forcontrolling an economizer includes a means for sensing characteristicsof air located in a mixed air section of an air handler, and a means forcontrolling a damper to control the air flow of outside air andre-circulated air in accordance with sensed characteristics of the air.

[0010] There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

[0011] In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the arrangements of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced andcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein, as well as the abstract,are for the purpose of description and should not be regarded aslimiting.

[0012] As such, those skilled in the art will appreciate that theconception upon which this disclosure is based may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out the several purposes of the present invention. It isimportant, therefore, that the claims be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an illustration of one embodiment of the invention.

[0014]FIG. 2 is an illustration of another embodiment of the invention.

[0015]FIG. 3 is a chart showing the results of a study for economizersserving a retail space.

[0016]FIG. 4 is a graph illustrating a pattern of CO2 buildup.

[0017]FIG. 5 is a flow diagram showing an embodiment of economizercontrol.

[0018]FIG. 6 is a graph of enthalpy per pound of dry air.

[0019]FIG. 7 is a graph of enthalpy per pound of dry air with a shadedregion showing a 50% loss with a change of 10 degrees.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0020] One embodiment of the invention includes the use of system supplyair pressure to move an air sample to an air return sensor, therebyenabling use of same sensors for measurement of one or more air qualityparameters for both supply air and return air measurement using pressureto drive reciprocating sampling. One such embodiment of the invention isgenerally illustrated in FIG. 1.

[0021]FIG. 1 illustrates an HVAC system or air handler having aneconomizer control in accordance with one embodiment of the invention.The HVAC system or air handler includes a fan 100, heating coil 102 andcooling coil 104. A supply air duct 106 leads to the space or buildingto be supplied air. A return air duct 108 leads from the space beingsupplied air back to a mixed air chamber 110 through a return air damper112. An exterior air damper 114 is provided between the mixed airchamber 110 and exterior air. In this embodiment of the invention, anactuator 116 is provided to open and close return air damper 112 andexterior air damper 114. A controller/sensor 118 is located betweensupply air duct 106 and return air duct 108. Based on the positions ofreturn air damper 112 and exterior air damper 114, controller/sensor 118will receive exterior air, return air or a mix of exterior air andreturn air through conduits 120. In some instances, return air damper112 may be closed so that return air cannot enter mixed air chamber 110.In this case pressure relief damper 122 opens to exhaust the return air.

[0022] Control/sensor 118 controls fan 100, heating coil 102 and coolingcoil 104. Return air damper 112 and exterior air damper 114 are alsocontrolled by control/sensor 118 using actuator 116. In one embodimentof the invention a thermostat/CO2 sensor 124 relays information tocontroller/sensor 118 to control the characteristics of air beingsupplied.

[0023] In another embodiment of the invention as depicted in FIG. 2, theHVAC system or air handler includes a fan 200, heating coil 202 andcooling coil 204. A supply air duct 206 leads to the space or buildingto be supplied air. A return air duct 208 leads from the space beingsupplied air back to a mixed air region 210 through a return air damper212. An exterior air damper 214 is provided between the mixed airchamber 210 and exterior air. In this embodiment of the invention, anactuator 216 is provided to open and close return air damper 212 andexterior air damper 214. A controller 218 is located between supply airduct 206 and return air duct 208. In some instances, return air damper212 may be closed so that not enough return air enters mixed air chamber210. In this case pressure relief damper 222 opens to exhaust the returnair.

[0024] Controller 218 controls fan 200, heating coil 202 and coolingcoil 204. Return air damper 212 and exterior air damper 214 are alsocontrolled by controller 218 using actuator 216. In one embodiment ofthe invention, a sensor 224, which could be a temperature/absolutehumidity sensor, receives outside air, return air or mixed air based onthe positioning of return air damper 212 and exterior air damper 214.The sensor 224 then relays information to controller 218 to control thedampers for proper airflow.

[0025] The invention as described above is capable of configuration inseveral embodiments for use in several different HVAC system economizercontrol applications. One such application concerns the improvedeconomizer control of unitary equipment. Another embodiment of thepresent invention results in the improved control of other HVAC systemssuch as unit ventilators, to control conditions within a classroom orhotel room. The present invention may take the form of a deviceintegrated into a unit ventilator or similar system, or as a wall orsurface mounted control.

[0026] One or more of sensors for smoke and measurement of other airquality parameters including temperature control rely on imbeddedmicro-processors for their measurement and control functions. Oneembodiment of the present invention enables the integration of many orall of these functions into a single device that can sharemicroprocessing power enabling multi-parameter sensing which results inan increased understanding of what is happening in a building, andthereby provides better control of the indoor building environment.

[0027] The present invention enables the use of CO2 level measurementsin return and supply air to calculate and set the outside air damperposition. The current invention also facilitates input and control ofremote CO2 sensors.

[0028] Carbon dioxide (CO2) is one of the common constituents of the airin our atmosphere. The concentration of CO2 in our atmosphere istypically 380 to 400 parts per million. Due to the natural tendency ofgas molecules to readily diffuse and equalize in air, worldwide levelstend to remain relatively constant and generally within theaforementioned range of concentrations. Because the outside CO2 level isrelatively constant, the outside CO2 level can be used as a referencevalue for outside air.

[0029] CO2 is also produced by humans at a relatively constant andpredictable rate based on a given activity level. An individual exhalesapproximately 40,000 PPM of CO2 with each breath. A more activeindividual contributes even more CO2 to a given space. Since people arethe most significant contributor of indoor CO2, the concentration levelof indoor CO2 is a good indicator of occupancy within a space. Forexample, doubling the number of people in a space will also double theamount of CO2 produced in the same space.

[0030] An inside measurement of CO2 concentration levels provides adynamic means to measure the number of people occupying a space(contributing CO2) and the amount of low concentration of outside airbeing drawn into the space to provide fresh air and dilute contaminants.As a result, CO2 can be used to measure and control the amount ofoutside air that is provided to the space.

[0031] Because the CO2 contribution is very predictable based on acommon activity level, the measure of CO2 is directly related to thecfm/person of outside air delivered to the space.

[0032] When CO2 control is applied to a unitary air handling system, CO2can be measured in the return air before the air intake dampers and/orin the space. The CO2 sensor is then used to modulate the outside airdamper to deliver the proper amount of outside air for the occupancy ofthe space. Typically this approach allows the damper to be adjustedbelow the fixed position typically set assuming “design occupancy”.Energy savings are realized here because a portion of outside air doesnot have to be conditioned. Yet the required ventilation ratesestablished on a per person basis can still be maintained thus ensuringacceptable indoor air quality. A CO2 sensor modulates the air intakedamper between an upper limit (typically 20-30% outside air) and a lowerlimit of about 5% outside air.

[0033] Another benefit is that the invention enables use of H2O levelmeasurements in return and supply air to calculate differential enthalpyand/or to control to dewpoint conditions.

[0034]FIG. 3 is a chart showing the results of a study for economizersserving a retail space. FIG. 3 shows the relative HVAC cost using noeconomizer, a 55 drybulb economizer system, a 65 drybulb economizersystem, an enthalpy economizer system and a differential enthalpyeconomizer system. The study revealed that drybulb economizer systemsshowed HVAC cost savings over a system without an economizer system. Thestudy revealed that both enthalpy based economizer systems showedgreater cost savings than the drybulb based systems and that thedifferential enthalpy system provided the most HVAC cost savings.

[0035] One embodiment of the invention includes a sensor to be affixedto a building or one of the interior walls of a space (such as abuilding or a room) to measure temperature, absolute humidity and CO2levels. The aforementioned air quality parameter measurements are usedto 1) sense occupancy within the space (CO2)2) control outside airventilation in the space (CO2) 3) maintain humidity levels below thepoint where moisture related damage may occur when the room isunoccupied and 4) to maintain temperatures when the room is occupied.This particular embodiment is particularly useful to monitor and controlspaces like but not limited to hotel rooms where occupancy isunpredictable and current control schemes strictly operate the system inan on/off mode.

[0036] The invention enables use of a CO2 level sensor for occupancydetermination within a space. The invention determines occupancy withina space by comparing CO2 concentration levels over a period of time anddetecting patterns in the variations of the concentration levels thatare typical of one or more people in the space. Such a sensor could alsobe combined with a simple occupancy sensor that could indicate initialoccupancy and the CO2 sensor could measure and control for on-goingoccupancy.

[0037] The invention also could be coupled with a simple occupancysensor to provide a baseline for initial occupancy of the space andwhere the invention measures occupancy continuously and controls theHVAC system to maintain the proper ventilation rate accordingly.

[0038] The invention enables use of a CO2 sensor in the measurement andcontrol of ventilation rates on a per person basis. CO2 levels in aspace increase to a predictable level in a predictable exponentialmanner to a CO2 level that corresponds to a given ventilation rate perperson in the space. Conventional CO2 control and measurement approachesgenerally must wait for CO2 levels to reach the peak or leveling offpoint of CO2 concentrations (called the equilibrium level) beforeventilation rates can be accurately predicted. FIG. 4 shows this patternof CO2 buildup and leveling off depending on the ventilation rate. Thepresent invention, however, uses a predictive algorithm to look at therate of rise of CO2 and predict where the leveling point or equilibriumlevel was and allowing a prediction of the current ventilation rate.This method of measuring ventilation overcomes the traditional problemof waiting for CO2 levels to build up and level off, instead providing areal time indication of the ventilation rate within the space. Thecalculation is based on the rate of change of CO2 over a fixed period oftime ranging from one minute or less to every 15 minutes or more.Variables of the predictive algorithm include the human activity levelanticipated in the space, the typical design densities expected, and themathematical function for the exponential buildup of CO2 concentrationlevels within a space. The invention allows for calculation and controlon a real-time basis of the actual ventilation rate/person to the space.This could be used both as a control parameter and a display parameterto occupants of the space. Such a parameter could also be indicated on adisplay in a graphical format which would indicate if a space was overor under ventilated or ventilated just right. It would provide a muchmore relevant indication of ventilation as compared to providing just aCO2 concentration.

[0039] In the present invention, sensors can be placed in the return airto compare differential conditions by adjusting dampers to allow aproper measurement of exterior air to determine if outside temperatureand humidity conditions (combined measurement is often called enthalpy)are sufficient to utilize outside air for free cooling. If sensors areprovided outside, the sensors would not last long due to the extremeconditions they are exposed to. Another embodiment of the presentinvention includes an absolute humidity sensor and temperature sensor inthe mixed air section of the air handler or air handling system. In thisarrangement, the sensors continually monitor the conditions of themixture of return air and supply air.

[0040] One such control strategy, as depicted in FIG. 5, controls aneconomizer as illustrated in FIG. 2. In step 500, the economizer is incooling mode. In step 502 the controller 218 periodically opens theexterior dampers to a consistent position above the current or minimumairflow setting. In step 504, the temperature detected by sensor 224 istransmitted to controller 218 to make a determination as to whether thetemperature is within an acceptable range for economizer control (e.g.between 55 F. and the return air temperature (70 F.)). If thetemperature is not within an acceptable range the exterior air intakedamper 214 is returned to a minimum air flow position in step 506. Ifthe temperature is within an acceptable temperature range, the absolutehumidity is determined in step 508 from sensor 224. If the absolutehumidity concentration is within an acceptable range, the external airintake damper 214 continues to open in step 510. Otherwise, the exteriorair intake damper 214 returns to a minimum air flow position.

[0041] Another variation of this approach is designed to only continueopening of the damper if temperature is acceptable and the absolutehumidity level remains the same or is dropped. If the temperature and orthe absolute humidity levels increase, the dampers or outside airflowrate will go back to the minimum position. If outside air is used forcooling, CO2 control of the dampers can be overridden by the economizercontrol.

[0042] The sensor in the mixed air may also be used to sense and controlthe latent heat and sensible heat cooling characteristics of an airhandling system by determining the moisture level of air before itenters the cooling coil. The ability for the coil to cool or removehumidity from the air can be controlled by a number of factorsincluding: controlling the velocity of air through the coils,controlling the temperature of liquid in the coils, or staging theoperation of a multiple combination of coils to achieve the desiredperformance level. This allows for much better control of humiditylevels than current control methods provide.

[0043] Humidity buildup in buildings in summer or any time in humidclimates can occur when equipment is placed on a setback or off cycleduring evening and weekends. As long as the temperature remains high,humidity concentrations are not a concern. However, when a system isactivated and cooling begins, the temperature will be reduced,significantly reducing the moisture holding capacity of the air. Theresult is that condensation will occur on the coldest parts of thebuilding (such as on slab on grade floors, around cooling ducts). Thiscondensation can lead to mold and mildew contamination that can affectair quality.

[0044] The conditions necessary to cultivate a hospitable environmentfor bacterial or fungal growth include warm temperatures (temperaturesof 60° to 90° ), availability of source of nutrients (dust, dirt andorganic human byproducts), and the presence of bacterial or mold spores(they come from outside but are everywhere), all of which are readilyavailable in most indoor environments. The missing ingredient that makesit all work is and enzyme solvent, namely water. When conditions in abuilding reach a point where water condenses on a cold surface in abuilding the final ingredient to a self-starting science project hasbeen added. Once this growth starts, the contamination will continue tosurvive regardless of the future presence of water.

[0045] Air has a limited capacity to hold water vapor based on itstemperature. As illustrated in FIGS. 6 and 7, if the air temperaturedecreases just 10° F., the air loses half of its ability to holdmoisture. Once air becomes saturated, it will condense on the coldestsurfaces. It is exactly the same effect that occurs to a cold drink heldin the humid summer air.

[0046] In a building it's a bit more complicated but the same principleapplies. When a room is unoccupied and the system is turned off, theroom heats up and humid air from outside enters the room. Because theair is warm it can hold lots of moisture. But when the cooling systemturns on, the air conditioning quickly cools the room to the set-pointtemperature. Unfortunately the system is unable to dehumidify the roomas fast as it cools the room and as a result, water begins to form onthe coldest surfaces in the room. The coldest surfaces of a room caninclude areas such as those on and around the air conditioner,slab-on-grade floors (in the carpets) and on bathroom fixtures. Watervapor that has seeped into walls and furniture within the space alsoreaches the condensation point and begins to break down the material.Humid air that has seeped behind the walls through electrical outletsand other pathways now starts to condense inside the walls on therapidly cooling drywall further helping its deterioration and allowingunseen microbes to grow unhindered.

[0047] The best way to avoid all these problems is to never allow watervapor levels to build up in a space so that condensation can occur whenthe room reaches its cooling set-point. In one embodiment of the presentinvention absolute humidity is measured in the space so as not to allowabsolute concentrations of water vapor to exceed a certain thresholdthat will result in condensation occurring at normal daytime coolingtemperatures.

[0048] The many features and advantages of the invention are apparentfrom the detailed specification, and thus, it is intended by theappended claims to cover all such features and advantages of theinvention which fall within the true spirits and cope of the invention.Further, since numerous modifications and variations will readily occurto those skilled in the art, it is not desired to limit the invention tothe exact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

What is claimed is:
 1. An economizer control comprising: a sensor thatsenses characteristics of air; a damper located relative to said sensorso that said damper can control air flow of outside air andre-circulated air to said sensor; and a controller in communication withsaid sensor and said damper, said controller opening and closing saiddamper according to conditions sensed by said sensor.
 2. The economizercontrol as recited in claim 1 wherein said damper comprises: an outsidedamper that allows outside air to enter a mixed air section of an airhandler when said outside damper is open, and prevents outside air fromentering the mixed air section when said outside damper is closed. 3.The economizer control as recited in claim 1 where said dampercomprises: an inside damper that allows re-circulated air to enter amixed air section of an air handler when said inside damper is open, andthat prevents re-circulated air to enter the mixed air section when saidinside damper is closed.
 4. The economizer control as recited in claim 1wherein said sensor measures temperature, enthalpy and occupancy level.5. The economizer control as recited in claim 1 wherein said sensorcomprises: a temperature sensor, an absolute humidity control sensor anda CO₂ sensor.
 6. The economizer control as recited in claim 1 whereinsaid controller adjusts said damper to limit the amount of outside airentering a mixed air section of an air handler when said sensor senses ahumidity level above a predetermined range.
 7. The economizer control asrecited in claim 1 wherein said controller adjusts said damper to limitthe amount of outside air entering a mixed air section of an air handlerwhen said sensor senses a temperature outside a predetermined range. 8.A method for controlling an economizer comprising the steps of: sensingcharacteristics of air; and controlling a damper to control the air flowof outside air and re-circulated air in accordance with the sensedcharacteristics of the air.
 9. The method as recited in claim 8 whereinsaid step of controlling the damper comprises the steps of: opening anoutside damper to allow outside air enter a mixed air section of an airhandler; and closing the outside damper to prevent outside air fromentering the mixed air section.
 10. The method as recited in claim 8wherein said step of controlling the damper comprises the steps of:opening an inside damper to allow re-circulated air to enter a mixed airsection of an air handler; and closing the inside damper to preventre-circulated to enter the mixed air section.
 11. The method as recitedin claim 8 wherein the step of sensing characteristics of air comprisesthe step of sensing the temperature, enthalpy and occupancy level. 12.The method as recited in claim 8 wherein the step of sensingcharacteristics of air comprises the step of sensing the temperature,absolute humidity and CO₂ level of the air.
 13. The method as recited inclaim 8 wherein the step of controlling the damper comprises the step ofadjusting the damper to limit the amount of outside air entering a mixedair section of an air handler when a humidity level above apredetermined range is sensed.
 14. The method as recited in claim 8wherein the step of controlling the damper comprises the step ofadjusting the damper to limit the amount of air entering a mixed airsection of an air handler when a temperature outside a predeterminedrange is sensed.
 15. A system for controlling an economizer comprises: ameans for sensing characteristics of air located in a mixed air sectionof an air handler; a means for controlling a damper to control the airflow of outside air and re-circulated air in accordance with sensedcharacteristics of the air.
 16. The system as recited in claim 15wherein said means for controlling the damper comprises: a means foropening an outside damper to allow outside air enter a mixed air sectionof an air handler; and a means for closing the outside damper to preventoutside air from entering the mixed air section.
 17. The system asrecited in claim 15 wherein said means for controlling the dampercomprises: a means for opening an inside damper to allow re-circulatedair to enter a mixed air section of an air handler; and a means forclosing the inside damper to prevent re-circulated air from entering themixed air section.
 18. The system as recited in claim 15 wherein saidmeans for sensing characteristics of air comprises a means for sensingtemperature, enthalpy and occupancy level of the air.
 19. The system asrecited in claim 15 wherein said means for sensing characteristics ofair comprises a means for sensing the temperature, absolute humidity andCO₂ level of the air.
 20. The system as recited in claim 15 wherein saidmeans for controlling the damper comprises a means for adjusting thedamper to limit the amount of outside air entering a mixed air sectionof an handler when a humidity level above a predetermined range issensed.
 21. The system as recited in claim 15 wherein said means forcontrolling the damper comprises a means for adjusting the damper tolimit the amount of air entering a mixed air section of an handler whena temperature outside a predetermined range is sensed.